Date of Award

Spring 1983

Document Type

Thesis

Degree Name

Master of Science in Chemical Engineering - (M.S.)

Department

Chemical Engineering and Chemistry

First Advisor

Joseph W. Bozzelli

Second Advisor

Barbara B. Kebbekus

Third Advisor

Gordon Lewandowski

Abstract

The reactions of various chlorinated hydrocarbons with molecular hydrogen or water vapor have been studied in a microwave plasma tubular flow reactor. The investigation of such reactions is desirable because the often toxic parent chlorocarbons are transformed to more thermodynamically stable and relatively non-toxic products by removal of' chlorine atoms as hydrogen chloride. Present detoxification technologies generally employ thermal oxidation as a means of disposal of chlorocarbons, which does not offer a thermodynamically stable sink for the chlorine atoms.

The experimental apparatus included feed introduction systems, a microwave plasma reactor, and full product analyses. The feed systems enabled use of gases and vapors from both relatively volatile and non-volatile liquids. The microwave plasma offers an interesting and unusual approach to chemical reactions. Because of the reactivity of such a discharge system, reactions are achieved to significant conversion levels without the high temperatures required in a conventional thermal reactor. Full product analyses were performed with flame ionization and thermal conductivity gas chromatography, mass spectrometry, and pH detection for HC1.

The reaction systems studied were chloroform / molecular hydrogen, trichloroethylene / molecular hydrogen, trichloroethylene / water vapor, and mono-chlorobenzene / molecular hydrogen. Ranges of conversions of the parent chlorocarbons were achieved, in some cases as wide as 50 to nearly 100 percent. Product analysis indicates conversions to hydrogen chloride, light hydrocarbons, and non-parent chlorocarbons when molecular hydrogen is used. Use of water vapor as a hydrogen source yields similar results, except that carbon monoxide replaces many of the light hydrocarbons. With either molecular- hydrogen or water vapor present, at least 85 mole percent of the chlorine atoms in the converted parent chlorocarbons form thermodynamically stable hydrogen chloride for parent conversions of 80 percent or more. The remaining chlorine atoms in the converted parent were present as non-parent chlorocarbons.

Water vapor was more effective than molecular hydrogen in decomposing trichloroethylene. The amount of water vapor required for a given conversion was an order of magnitude smaller than the required hydrogen. The overall rate constant for the water reaction was about double that for hydrogen at comparable electric input power levels. When their relative cost is also considered, water vapor would appear to be much more desirable for a commercial process.

In addition to full product analysis, preliminary kinetic analyses were performed with reaction mechanisms postulated. The reactions in the plasma were found to follow one-half order kinetic dependence on each of the feed reagents. The plasma reactor exhibited reactivity which varied in an Arrhenius fashion with input electrical power to the microwave generator.

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